Teletypewriter switching system



Sept. 12, 1950 c. R. WALKER 0 TELETYPEWRITER SWITCHING SYSTEM Filed Aug. 2, 1948 5 Sheets-Sheet, 1

F/GJ F1621 FIG. .1 F164 Fla:

INVENTOR C./?. WALKER ATTORNEY Se t. 12, 1950 c R..WALKER 2,522,003

' TELETI'YPEWRITER SWITCHING SYSTEM 7 7 Filed Aug. 2, 1948 5 Sheets-Sheet 2 irllll 5/ m/vzzvr'oz? BY C. R. WALKER.

ATTORNEY Sept. 12, 1950 TELETYPEWRITER SWITCHING sysmu Filed Aug. 2, 1948 c. R; WALKER I 5 Sheets-Sheet 3 FIG. 3

i SUB- 87A TION Q T I SUB-5 TA T/ON R UF u@ m/vavron CR. WALKER ATTORNEY Sept. 12, 1950 v c. R. WALKER .2; 2,522,003

"rmiE'TiPEwRmga SYWITCHINC? SYSTEM:

Filq Au 2, 194a 5 Sheets-Shc 4 Flu-I /2 III! /N VE N TOR C. R. WALKER A TTORNEV ingrelays'if'any is operated.

Inaccordance with a preferred embodiment Patented Sept. 1 2, 195

UNITED STATES I FFICE 2,522,003 7' TELETYPEWRITER swn' mset'srsrmi Charles Robert Walker, J erse'y' City, N ".I assignor to American Telephone and Telegraphflompany, a corporation of NewXonk Application August 2, 194 Serial No. 41;:24'4

This invention relates to telegraphy and particularly to teletypewriter switching systems.

An object of the invention is to connect any one or group or all of a plurality of receiving stations to a telegraph channel to receive mes sage material transmitted over the channel.

Another object of the invention is to disconnect from the channel any connected one-of the receiving stations only upon the selective con- --nection of another station to the channel so that atno time is the telegraph channel without a connected receiving station.

Another object of the invention is to disconnest anyc'onnected one of the receiving-stations incident to the selective connection of another "station to the channel.

Another object of the invention is to provide aplurality of switching stations associated with a-communication channel, each serving a plurality of receiving stations, and being so arranged that when a switching operation takes place at one of the switching stations to connect one of its receiving stations to the telegraph channel, any receiving station then connected to the channel, whether served by that switching station or another switching station, will be automatically disconnected from the channel.

The invention features the use of telegraph signal controlled switching instrumentalities for selectively connecting receiving stations to the telegraph channel in response to station designating or switching code signals.

The invention also features relay circuits-and locking circuits therefor for connecting the receiving stations to the telegraph channel under one switching station so that the selective operation of one such relay at a stationwill cause to be interrupted the locking circuits'of all other switching relays at that switching station.

The invention also features an'arrangement whereby the switching instrumentality at each switching station, upon responding to switching signals assigned to receiving stations served by other switchingstations, unlocks its own switchof the invention a message originating point or station has transmitting equipment connected to a telegraph line or'channel'extending toone or more switching stations, eachof which :has

signal responsive equipment associated with'the Claims. (Cl. MS- 2) 2 g one channel. Each of the switching stations is providedwith a permutation code selector mech- 'anism having contacts arranged to beselectively closed momentarilyin response to permutation code signals transmitted over the telegraph channel from the message originating station. These "contacts are arranged to control the circuits of switching relays. Certain relays perform a preparatory or activating function and "are operative by contacts in the permutation code selectorm'echanism'if operated in predetermined order or sequence in response to their 'code signals, namely, Figures and H, received'in that sequence, to associate with station selecting contacts of "the permutation code selector mechanism, individual switching relays that are operable to connect to the-telegraph channel indivi-dua'l lines extending to receiving stations.

After the activating relays have beenoperated,

the next received signal, if'it represents a particular receiving station to be selected, will operate its assigned contact in the permutation code selector mechanism and if the signal represents a receiving station served by that switching sta- 'tion, the associated switching relay will be operated'to connect the selected line to the telegraph channel and this relaywill be lockedin the operated condition.

The locking circuits for the switching relays are interrelated, so that only one of them etc.

switchingstation may be locked at any one time.

Any such relay upon operating interrupts the locking circuits of all others and releases any that-may have been lockedatthe time it operated. The code which follows a line selecting code is the Letters signal and the receptionof this code results in the deactivation of the switching system by effecting the release of the preparatory -or activating relays. The letters signal is followed by the message, which will he received by the receiving station associated'with the connected line. Although the permutation code selector mechanism receives all signals contained in the body of the message, 'no further switching operations occur because the switching mechanism-has been deactivated.

tions is again transmitted to prepare for the selective connection of another line. Ifthel'ine tobe selectively connected 'is served bythe same switching office, the operation of its switching relay will result in the interruption of the looking circuit for the previously operated switching relay and that relay will be released.

When two or more switching stations are provided, each having lines to be connected to the telegraph channel, contacts in the permutation code selector mechanism at each switching station that are operable, in response to selecting code signals for lines served by other switching l adotted -line rectangle designated by the referstations are connected in multiple to the operating circuit of a release relay to release any operated switching relay thereat. In this way the selective connection of a line to the communication channel anywhere in the system will re suit in the disconnection of a previously connected line anywhere in the system.

With an arrangement as hereinbefore de' scribed in which a line may be disconnected only.

incident to the connection of another line, at no time is the telegraph channel without a connectence numeral H represent a teletypewriter printer and keyboard transmitter comprising a unit which may be of the type shown in Patent 1,904,164 granted April 18, 1933 to S. Morton et a1. and the disclosure of the Morton patent is incorporated herein by reference as part of the present specification. The keyboard transmitter is represented symbolically by the transmitting contacts i2 and the teletypewriter printer is ed line and it is notpossible for messages to be completely lost because a message not preceded by a selecting code signal will be received at the station which was last selected to receive a message.

In addition to the individual line connecting relays at each switching station there may be one or more group or broadcast switching relays which have their locking circuits intercontrolled by all of the individual line selecting or switching relays in the same way that'their looking circuits are interrelated. The signal responsive contacts which operate the broadcast or group switching relays are responsive to the same code signal at all switching stations serving lines involved in the group. Upon the transmission of the broadcast code signal following the activating signal sequence, the broadcast switching relay at each switching station will be operated to connect to the telegraph channel all lines served by that switching station that are included in the group and each such relay will look operated, and at that switching station which hadan individual switching relay locked for the reception of a previous message, such relay will be released, the

station, however, if included in the group, re-

maining connected because the broadcast switching relay is operated. Also, when the broadcast relays are locked, and the broadcast message has been completed, and thereafter code signals are transmitted to select an individual line served by a switching station, the broadcast relay will be released by the direct interruption of its locking circuit by the selected individual switching relay at that switchingstation and at other stations the broadcast relays will-be released by the operation of the release relay due to the reception of a selecting code which is not assigned to any of the receiving station lines served by those switching stations. v

For a complete understandingof the invention reference may be had to the following detailed description to be interpreted in thelight of the accompanying drawings in which:

Figure 1 is a view showing the circuits of a message originating station;

' Fig. 2 is a view showing the circuits of a switching station; v

Fig.3 is a view showingthe circuits of receiving stations associated withtelegraph lines served by the switching station in Fig. 2; g i Fig. 4 is a view showing the circuits of a second switching station; w

Fig. 5 is a view showing diagrammatically the represented symbolically by the magnet i3 which is the selector magnet of the printer and is responsive to signals to cause the printing ofcharactors or the accomplishment of functions corresponding to the signals. In addition to the keyboard transmitter 12, the station may also be provided with a tape transmitter M. This transmitter may be of the type shown in Patent 2,055,567 granted September 29, 1S36 to E. F. Watson, and .the disclosure of this patent is incorporated herein by reference as part of this specification. The transmitter comprises an outer segmented ring including start, code and stop impulse segments, the code impulse segments being connected to tap sensing contacts I6, a continuous or closed inner conductive ring, interconnected brushes engaging the outer and inner rings of the distributor and carried by brush arm H, a driving shaft l8 to which the brush arm I! issecured, a motor 29 for driving shaft l8 through friction clutch ';2I and .astop cam 22 for arresting shaft 18 under the control of stop magnet 23. Perforated tape containing signals to be transmitted by transmitter I4 may be supplied by keyboard perforator 24 which may be of the type shown in Patent 1,182,179 granted May 9, 1916 to C. L. Krum et al. Perforated tape passing from keyboard perforator 24 to tape transmitter i4 is engaged by a taut tape member 26 which closes contacts 2'! when a loop of tape of predetermined dimensions has been formed. Ii manual switch 28 has been closed prior to the formation of the loop, a circuit will be traced upon the closeure of contacts 21 from battery 29, through switch 28, contacts 21 and winding of magnet 23 to ground, to disengage the armature of stop magnet 23 from stop cam 22 and permit shaft l8 to be driven by motor l9.

A circuit is traced from battery 3! through the stop or rest contacts of keyboard transmitter l2 when that transmitter is at rest, selector magnet l3 of the teletypewriter printer, stop or rest segment, brushes and closed ring of transmitter l4, conductor 32 and operating winding of transmitting relay 33 to ground to hold selector magnet l3 energized and to hold relay 33 operated to its marking contact. Relay 33 has a biasing winding provided with a battery connection to drive the armaturetothespacing contact when the operating winding is deenergized, the operating winding predominating when it is energized and holding the armature of the relay on its making contact. Marking impulses generated by keyboard transmitter I2 or tape transmitter I ,4 provide a closed circuit condition for selector magnet l3 and transmitting relay 33 to hold the selectormagnet in the marking condition and to holdlthearmatureof relay'fl on its marking contact. Spacing signals generated by keyboard transmitter l2 or tape transmitter M are represented by an open circuit conditiomreleasing se- =lectormagnet l3 and permitting the armature or-transmitting relay 33 to engage-the spacing contact. Selector .magnet 13 of the teletype- "writer printer responds to signals generated by 'keyboard transmitter I2 or tape transmitter l4 andprovidesaprinted record of messages asthey,

are transmitted. It will be understood that'mes- =sagesmay be transmitted from either transmit- -ter, but that both may not be operated simultaneously.

The-marking and-spacing contacts of transmity 'ra h line 34 may extend to and' through other "switching stations 'such'as the station indicated diagrammatically in Fig. 5 by the reference number Ml, and ultimately terminates at ground potential.

Since the transmitting relay 33 transmits polar sign'als thereceiving relays 36, 31, 38, 39, l l l, H2 and ll3are polar relays. With polar operation of'such relays, it is not essential that they be I provided-with biasing windings but they may be soequipped' and battery potentials of the proper polarity maybe supplied to those windings as in- =clicated in Figs. 2 and 4.

The armature of relay 36 is connected to bat tery 5i and the marking contact is connected to ground through the winding of the selector mag- -net"52"of a contact operating permutation code selector mechanism or monitoring selector. A device of this type is shown and described'in detail in Patent 2,112,234 granted March 29, 1938 to F. Beattie et al. and the disclosure of this patentis incorporated herein by reference as part of the present specification. The structure of the monitoring selector equipment employed in this invention is substantially the same as that disclosed in the Beattie patent and operates in substantially the same manner. Its function is to sclose electrical contacts selectively and momentarily in response to the reception of telegraph signal code combinations.

It will be assumed that keyboard transmitter l-z-is operated to select a particular receiving stationand transmit a message thereto, or that a tape containing such a message has been pre- .-pared in keyboardyperforator 24 and that tape -rtransmitter It has been started. The sequence of code combinations transmitted is Figureathe l'etterI-I, a letterof the alphabet representing the designation of the. station to which the message directed, Letters and the message itself.

Upon the reception'of the codecombinations mepresentingFigures the contacts 53 close mo- =mentarily. Contacts 54 also close momentarily, these being universal contactsthat are operated each time the monitoring selector receivesa code combinationregardless-of the selective nature of that f code combination.

. A circuit is traced from ground through closed -IB contact '53, conductor :5'6,.lower winding of relay 451 to conductors :58 and "60, 'upper winding ,'0f relayz59 toxzbattery 6|. .Relay51 .operates andat its inner .lower armature and front contact it completes a circuit, during the time that uni- "versalscontacts5i remain closed, from battery through "the closed contacts 54', the noted-armature an'd front contactof relay 51 and the lower winding of relay 59 to battery 62. It follows from this that both windings of relay 59:become'ener- 'gized, the upper winding first and then the lower winding. The lower winding of relay 59'seeks topperate'the armature of that relay to its first contact but the upper winding predominates and 'holds the armature on its back contact.

'The relay 51also completes for itself'a holding circuit'traced from battery 63 through the upper 'windingofthat-relay; the inner upper front contactan'd armature, conductor H, the back'contact and armature of relay 59, conductor 6'8, and the outer lower armature and-front contact of relay-51 to ground. At its outer u-pper armature the relay 51 prepares an energizing circuit for relay M. Upon'the opening of contacts 53 and ['54 of the monitoring selector, the lower winding 'ofrelay- 5T andboth windings of relay 59 become deenergized, relay 5'! remaining operated due to the previously traced locking circuit.

' The next code combination that should be and is presumed to be received is that representing theletter "H which will cause the momentary operation of contacts 86. These contacts complete a circuit from ground through the 'outer'upper front contact and armature of relay 5?, upper winding of relay G4, conductors 58'and lilland through the upper winding of relay 59 to battery 6|. Relay 64 operates through the energization "of'its upper winding, and the upper winding of relay '59 again becomes energized. in'series therewith. Contacts 55 again operate, completingthe energizing circuit for the'lower winding of relay 59 which remains unoperated due to the predominating effect of the upper winding.

'At its inner lower armature and front contact the'relay 64 completes for itself a holding circuit "traced from battery 59 through the lower winding of 'relay 64, the noted front contact and armature ofthatrelay, conductor ll, back contact and'armature of relay 59, conductor 68 and inner armature and front contact of relay 51 to ground, relay 64 thus being locked in parallel with relay "51 through the armature and back contact of relay 59. At the outer lower armature and front contact of relay 64 a ground additional to that supplied throughthe outer lower armature and front contact'of relay 5'! is connected through conductor 68 and the armature and back contact 'of relay-59 forlocking relays Hand '64, the addi- "tional ground being supplied for a purpose which =wi1l-be described later. 'At'lts remaining armatures the relay H prepares individual energizing circuits for the relays l6,'1'|,"l8,'19and8i.

Following the reception of the code combina- -'tion'for the letter "H and the operation-and looking of relay 64, the code combination for selecting au'eceiVings'tation will be received by selec- =tor*magnet52. It will be assumed that this code combination represents the letter R and the mo- -mentaryclosure of contacts 82 will occur. These contacts will-complete a circuit from'ground through the third upper armature and front contact of relay-t l, counting from the'top, conduc- 'tor 83Qlower winding ofrelay l! to conductor'58, downwardly-along that conductor to conductor fifl and through the upper windingof'r'elay fl to battery Bl. Relaylloperates over this circuit. 7, The operation of contacts 82 is accompanied by the closure of universalcontacts 54 which again complete a circuit from ground through conductor 55, the inner' lower armature and front contact of relay 5! and. the lower winding of relayeifl to battery B2.- The lower winding of relay 59 is again unable to operate the .relay because the upper winding is energized in series with the lower winding of relay 11.

Relay 11 completes for itself a locking circuit from battery 84 through conductor 86, the upper winding and inner upper armature and front contact of relay 11, innermost lower armature and back contact of relay 16, middle lower armatures and back contacts of relays 18 and 19, conductor 81 and armature and back contact of relay 8! to ground. It will be noted that the locking circuit just traced includes an armature and back contact of each of the relays 16, 18 and 19. It follows from this that upon the energization of any one of these three relays the locking circuit of relay 11 will be interrupted and that relay will be released as will be more fully described later. At its threelower armatures, relay 11 interrupts similar locking circuits individual to the three relays 16, 79 and 19 for the purpose of releasing any one of those relays that might have been operated and locked. At its outer upper armature and front contact the relay 11 completes a circuit from ground through the winding of relay 88 and conductor 89 to battery 9 l The relay 88 operates and at its upper armature, in make-before-brcak sequence, connects telegraph line 92 to the marking contact of receiving relay 38 and disconnects the telegraph line 92 from battery 93. Line 92 extends to receiving station 94 in Fig. 3 and is connected to ground through the winding of the selector magnet 96 of a teletypewriter printer which may be of the same type as the one designated H in Fig. l, and the selector magnet 96 is intended to represent such a teletypewriter printer. Since twovway transmission over telegraph line 92 is not contemplated, the teletypewriter at station 94 may not be equipped with transmitting mechanism, or if it is so equipped the transmitter will be arranged to transmit over some other communication circuit, not shown. The relay 88 also completes a circuit from battery 91 through its lower armature and front contact, signal conductor 98, winding of relay 99 at station 94 to ground. A circuit is completed by relay 99 from the left-hand terminal of battery the armature and front contact of relay 99 and the winding of relay 102 to the right-hand terminal of battery I01. Relay Hi2 operates and locks in a circuit through its upper armature and front contact and unlocking key 193. At its lower armature the relay I02 completes the circuit of signal lamp I94. By virtue of, the manually releasable locking circuit the lamp I04 will remain li hted after relays 11, B8 and 99 have been released, thereby serving to indicate that a message has been received.

The battery 93 in Fig. 2, which is connected to telegraph line 92 when relay 88 is not energized, holds telegraph line 92 closed and maintains selector magnet 98 energized which is the normal .idle condition when a message is not being trans- Returning to consideration of the monitoring T selector mechanism in Fig. 2, the code transmitted to and received by relays 36, 31, 38 and 39 next after the station selecting code is designated Letters.

The monitoring selector is not provided with contacts operable in response to this code, or if there are such contacts they are not employed in this system. In response to the reception ofthis code combination the universal conlower winding is enabled to operate the armature to the front contact which it does. As the armature of relay 59 leaves its back contact it disconnects. the locking windings of relays 51 and 64 from the duplicate ground connections supplied through their respective outer lower armatures and front contacts to conductor 58 and transfers those ground connections to its own lower winding, thereby establishing for itself a holding circuit. Since the holding circuits for relays 51 and 64 have been interrupted these relays release,

each disconnecting ground from. the holding circuit for the lower winding of relay 59 and when both ground connections have been disconnected the relay 59 will release. The purpose in trans- ,ferring the holding ground connections of relays mitted to the station 94. Upon the connection of telegraph line92 to the marking contact of relay 39, the selector magnet 96 is responsive to ltelegraph signals received over line 34 and repea ed r l y 38...

51' and 64 to relay 59 is to assure that relay 59 shall'not release solely as a result of the reopening of universal contacts 54, and the purpose in supplying the duplicate ground connections from relays 51 and 64 individually is to assure that relay 59 shall not release until after both of the others have released. The condition of the relay circuit in Fig. 2 at this time is that only the relays 11 and 88 are energized.

The next signal to be received will probably be carriage return and line feed signals, assuming that the teletypewriter printer with which station 9 5 in Fig. 3 is equipped, is a page printer, it being customary to make certain that the received message shall begin at the beginning of a new line on the paper in the teletypewriter printer.

"The monitoring selector in Fig. 2 has contacts "momentarily closable in response to the carriage return and line feed signals but no use is made "of these contacts in this system.

followed by the body of the message.

will repeat the message to receiving station 94 The carriage return and line feed signals are Relay 38 where it will be recorded. Selector magnet 52 of the monitoring selector also responds to these signals and the contacts corresponding to those signals will be operated, but none of the relays 16,18, 19 and Bi is able to respond to the operation of those contacts because their energizing circuits are open at front contacts of relay 84 which is released. The body of the message may include the Figures code combination and this will cause the operation and locking of relay 51.

-'I-l is not used in the body of a message since this sequence is used for activation of the switching relay system. In response to the next code combination, whatever it may be, and regardless of .76 Whetherornot .it .operatesany :of the contacts 9.; in the monitoringselector, the universal contacts '4' -will'completethe energiaing circuitof the lower winding of relay 59-which will operate andlock, interrupting the lockingcircuit of relay 51- which will release and thereby interrupt the locking circuit of relay 5-which will also release.

At the end of-the message, transmission ceases, leaving relays TI and 3,8 operated andtelegraph line 92 connected to the marking contact "of relay'38.

It will benoted that the telegraph channel 34 extends across Fig. 3 and into Fig.4 and that it hasrepeating relays;III, H2 and II 3: connected toit in series. The marking contactcf irelay I II is, connected through the winding of selector magnet 52 to, ground. The selector magnet {52' is the receiving instrumentalityof a monitoring selector, mechanism like that shown in Fig. .4. It has Figures contacts 53 for energizing magnet 51', contacts 65 .for completing the circuit of relay 64 and universal contacts 54' for completing the circuit of thelower Winding of relay 59,. It also has contact82. representing the, letter R corresponding to the contacts 82 in Fig. 2,.

- During thetransmission of. the codes for Figures and H which activated the relay switching sys-- tem in Fig. 2 preparatory to the operation of relay- 11 as previously described, relays 51 and 64 019-- erated and, locked in the same manner. When, the code combination .for R was receivedand effected the operation of contacts 82 and relay, 11 in Fig. 2, contactg82. in Fig. 4 closed.anolcornpleted a circuit from ground throughconductor II5 ,,the outermost upper armature and. front contact of relay 64; the windin of relay BI, conductor 58, conductor 60 and.the,upper.w inding of relay 59' to battery 6!. Relay 8| operatedby relay 59, did not operate because although its lower winding was energized in a circuit com.- pleted from contacts 54, the upper windin predominated and held it unoperated. Relay 8 I has no locking circuit and its function is to disconnect ground from. conductor 81. This conductor is common to the locking circuit of relays I2I, I22 and I23, so that had any of these relays been locked at, that time it would have been unlocked and released.

It will now be assumed that the next message to be transmitted is directed to a receiving station served by the switching station shown. in Fig. 4, this being the station I24 in Fig. 5. This station is selectable in response to the calling code combination representing the letter S. Accordingly, the sequence of code combinations pre-. ceding the message will be Figures, H, S, Letters, Carriage return and Line feed. In response to thecode combinations for Figures and H, relays 51 and 6.4 in Fig. 2 and relays 51 and 64' in Fig. 4 operate and lock, relays 59 and 59' remaining unoperated. The code combination for the letter 5 causes contacts I 26 in Fig. 2 and contacts I28 in Fig. 4 to operate. Contacts I25 complete a circuit from ground through the second armature and front contact of relay 64', counting from the top, lower winding of relay I2 I ,conductor 58' and upper winding of relay 59' to battery SI. Relay I2I locks in a circuit from battery 84- through conductor 86, the upper winding of re lay I2 I, the inner upper armature and front contact of that relay and a series path through armatures and back contacts of relays I22 and Q23 and conductor 81 to ground on the armature of relay 8|. Relay I2I completes the energizing circuit of relay I2! which connects telegraph line I28 of receiving station I24 to the marking contact of repeating relay H2. Relay I21 also connects bat: tery. tosignal conductor I29 to operate the signal lamp circuit: (not shown) atstation I24, which may be the same asthat described with respect to the receivingstation 94 in Fig. 3.

In: response to, the Letters code combination which follows the selecting code for. the station I24; the contacts 54 complete the energizin cuit for the-lower winding of relay 59 which opera ates because its upper winding is not concurrently energized and releases the relays 5.1, and 541', these relays in turn releasing relay 59'. Thereafter the signals of the message transmitted over telegraph, channel ,34 are received by station I24;

During the selection of station I24 in response to the activating codes Figures and. H and the station selecting codes the monitoring, selector of the switching station shown in Fig.2 responded to these codes, operating andlocking the relaysfil' and- 64 in response to the activating codes. '-The contacts I26 close in response to the station.selecting code S and complete a circuit from ground through thosecontacts, conductor II IS, the outermostupperarmature' and front contact of relay. 64, winding of relay 8|, conductors 5,3 and. upper winding of relay 59 to batterytl. Relay BI operates in series with the upper winding of relay' 59 and disconnects ground from conductor .8If which is included inthe, previously traced locking. path for relay 'I'I whichvoperated and locked. to connect-station 94 in Fig. 3 to repeating relay. 3% for reception ofthe preceding message. Relay II releases and in turngreleases-relay 8&therer. by disconnecting telegraph line 92from repeating relay stand reconnectingbattery 9.3 to. telegraph; line 92 to hold the teletypewriter printer at sta-v tion 84* in the normal idle condition. With this arrangement the telegraph line 92, havingbeen connected to received signals from telegraph, channel 34; remains connected and becomes disconnected, 'not in response to activation of the. monitoring selector at the switching station shown in Fig. 2'but only in response to the actual selective connection of another telegraph line. to receive signals from telegraph channel 34'.

Byreference to Fig.2 it will be noted that con-. tacts of the monitoring/selector responsiveto the letters S, Q, G, W; D and A are connected to con,-v ductor IIB so that upon the closure of any or those contacts" after the relay 64 has been operated, the relay 8| will be operated to openthe, lockingcircuit of any of'the relays 15, 11, 18. and. I9 that they may then be operated. These contacts are identified by the reference numerals I26, I36; I37, I38 and I39, respectively. The contacts I26 and I38, corresponding to thecontacts I26 and I 38, are effective, when relay 64' has been operated, to complete the operating circuits. of relays I2I' and I22 in Fig. 4.

There is shown diagrammatically in Fig. 5 a third switching station I4I serving receiving telegraph stations I42, I43 and I44 and having repeating relays I46, I41 and I48 associated with telegraph channel and. individual to the sta-- tions I42, I43 and M4 to repeat signals to those stations when selected. The switching station I41 also has repeating relay I49-associated with telegraph channel 34 for controlling the: monitoring selector at that station. The Sta,- tions I42, I43 and- I44 in Fig. 5 have been desig nated by the; calling codes G, W and A, respectively, andinresponse to these selecting codes the-contacts I36, I3Iand'I39 in Fig. 2. are oper able to-causethe operation of releasing'relay 8*I" when the relay B4 is operated. From this it follows that when any receiving station served by the switching station shown in detail in Fig. 4 or served by the switching station I4I indicated diagrammatically in Fig. is selected, the operation of the switching contacts at the station shown in Fig. 2 corresponding to those receiving stations will be operated to disconnect any station served by the switching station in Fig. 2 that may then be connected. Similarly, the stations designated by the calling codes Q, R and N' in Fig. 3, being served by the switching station shown in Fig. 2 and being selectable by the contacts I51, 82 and I52, the contacts IfiI, B2 and I52 and also the contacts I36, I31, and I39 at the switching station shown in Fig. 4 are connected to operate relay 8I' and disconnect any connected station served by the switching station shown in Fig. 4 when a station served by the switching station shown in Fig. 2 or Fig. 5 is selectively connected to receive signals. Finally, at the switching station shown in Fig. 5, the contacts responsive to the station selecting codes Q, R, N,.S and D would be connected to operate the release relay at the switching station shown in Fig. 5.

The system includes provision for the broadcasting of a message to all receiving stations. Such a message is preceded by the activating codes Figures, and H and the letter U. The relays 5! and 64 at the switching station in Fig. 2 and the relays 51' and 64 at the switching station in Fig. 4 and corresponding relays at the switching station MI in Fig. 5 will be operated. The selecting code U has been assigned to the broadcast selection, and in Fig. 2 a circuit will be. completed from ground through contacts I60, the innermost upper armature and front contact of relay 84, lower winding of relay I5, conductor 60 and upper winding of relay 59 to battery 8|. Relay I9 operates and locks in a circuit from battery 84 through the upper winding of relay I9, inner upper armature and front contact of that relay, middle lower armature and back contact of relay '16, innermost lower armature and back contact of relay 'II, outermost lower armatureand back contact of relay I8, conductor 81 and back contact and armature of relay 8| to ground. At its three lower armatures the relay I9 interrupts the locking circuits for relays I8, 11 and I8 so that if any of those relays has been inthe operated condition it will be released. Relay I9 also completes the energizing circuit for relay I6I through its outer upper armature and frontcontact. Relay I6I operates and connects ground through its three armatures and front contacts and through individual conductors to the windings of relays I62, 88 and I 63 and thence to battery 9|. Relays I62, 88 and IE3 operate and connect the three receiving stations in Fig. 3 to the repeating relays 31, 38 and 39 in Fig. 2

and also operates the signal circuits at the three receiving stations.

At the switching station shown in Fig. 4, the contacts I68 operate and complete a circuit from ground through the innermost armature andi'ront contact of relay 64, lower winding of relay I23, conductor 60' and'upper winding of relay 59' to battery BI. Relay I23 operates and locks in a circuit from battery 84- through conductor .86, the upper winding of relay I23, its inner upper armature and front contact, the inne -lower armature and back contact of relay I 2I, the, outer lower armature'and back contact qif-frelayl22, conductor 81' and back contact and armature or relays! to ground. At its lower armatures the relay I23 interrupts the locking circuits for the relays I 2| and I22 so that if either of these relays had been energized it will be released. At its outer upper armature and front contact relay I23. completes the energizing circuit for relay I65 which operates and completes circuits from ground through its armatures and front contacts, individual conductors, the windings of relays I21 and IE1, conductor 89' to battery SI. Relays I21 and I6! operate and connect the two receiving stations in Fig. 5 served by the switching station in Fig. 4 to the repeat, ing relays H2 and H3. Similarly, switching station I II in Fig. 5 will respond to the broadcast selection code to connect stations I42, I43 and I to repeating relays I46, I41 and I48, respectively. The Letters signal following the broadcast code will release relays 51 and 54 in Fig. 2, relays 51' and 64' in Fig. 4 and the corresponding relays of the switching station I in Fig. 5. The message that is thereafter transmitted will be received at all of the receiving stations. Upon the subsequent selection of a single receiving station to receive a message, such as the station 94 served by the switching station in Fig. 2, the broadcast selecting relay I9 will be released upon the interruption of its locking circuit at the innermost lower armature and back contact of station selecting relay 11. At the switching station shown in Fig. 4 broadcast selection relay I23 will be released by the operation of relay Si in response to reception of a station selecting code assigned at the switching station in Fig. 2 but unassigned at the switching station in Fig. 4 and therefore connected to conductor M6 to operate relay 8|.

It will be understood that additional receivin stations may be served by any switching station, the switching station in Fig. 2 being cited as an example, by the addition of relays corresponding to the relays I6, I! and I8 energizable through switching contacts now appearing unassigned in Fig. 2 and by the provision of additional locking circuit break contacts for the relays IE, IT, I8 and I9, one set of breakcontacts for each station selecting relay added to the switching station. At all other switching stations the corresponding switching contacts would be connected to operate the release relay, in the case of the switching station shown in Fig. 4, such contacts being connected to conductor II B.

It will also be understood that there may be, special circumstances under which there would be no occasion to transmit broadcast messages to certain receiving stations. It might, for example, be assumed that there is no occasion totransmit a broadcast message to the receiving station in Fig. 3 having the calling code Q. This station could be excluded from broadcast transmission merely by omitting an energizing circuit for relay I 62 from an armature and front contact of relay IBI. There also might be special system conditions under which it would be desirable to transmit messages of a certain type to specified receiving stations representing a group and other types of messages to other receiving stations representing a different group, with or without having certain of the receiving stations commonto both groups. This could be accomplished, again taking Fig. 2 as an example, by adding a relay corresponding to the relay I9, operable in response to a particular calling code, having its locking circuit under the control of all otherswitching relays and arranged to control the;

locking circuits of those relays, and also adding a relay corresponding to the relay 161 to complete the energizing circuits of those of the relays I88, 88, I68 and other like relays associated with the telegraph lines of receiving stations to be included in the group. Several relays corresponding to the relay 19 could be added to select various combinations of the relays I82, 88, I83 and others in response to group calling codes. Similar group switching relays could be added to other switching equipment such as the one shown in Fig. 4, to be operated in response to the selecting codes for those groups which included one or more receiving stations served by that switching station. At any switching station serving receiving stations, none of which is to be selected as part of a group, the monitoring selector contacts operable in response to the calling code signal of that group would be connected to operate the release relay, such as the relay 8| in Fig. 2 and the relay 81' in Fig. 4, for the purpose of disconnecting any receiving station telegraph line, served by that switching station, that might have been connected to receive the preceding message. It follows from all of the foregoing that the selection of any single receiving station telegraph line or group of those lines to receive a message will result in the disconnection anywhere in the system of any station or stations that were connected to receive the preceding message and are not to receive the current message.

Although a specific embodiment of the invention has been disclosed in the drawings and described in the foregoing specification, it will be understood that the invention is not limited to such specific embodiment but is capable of modification, rearrangement and substitution of parts and elements without departing from the spirit of the invention and within the scope of the appended claims.

What is claimed is:

1. In a telegraph switching system, a transmitter, a transmission channel associated therewith, a plurality of switching stations each having signal responsive switching means associated with said channel, a plurality of lines connectable to said channel at each of said switching stations, a receiving station associated with each of said lines, means controlled by the switching means at each switching station for selectively connecting the lines of that switching station to said channel, and switching elements for disconnecting any connected line only upon the selective connection of another of said lines to said channel.

2. In a telegraph switching system, a transmitter, a transmission channel associated therewith, a plurality of switching stations each having signal responsive switching means associated with said channel, a plurality of lines connectable to said channel at each of said switching stations, a receiving station associated with each of said lines, means controlled by the switching means at each switching station for selectively connecting the lines of that switching station to said channel, and switching elements at each switching station for disconnecting any connected one of its lines upon response of its switching means to signals assigned to connect one of the lines of another switching station.

3. In a telegraph switching system, a trans.

mitter, a transmission channel associated therewith, signal responsive switching means associated with said channel, a plurality of relays selectively operable by said switching means, line connecting elements controlled by said relays for connecting said lines to said channel, a looking circuit for each of said relays including break contacts controlled by all other of said relays whereby the operation of any one of said relays unlocks any one of them that is then looked in operated condition, and a locking circuit interrupter operable directly by said switching means for interrupting said locking circuits.

4. In a telegraph switching system, a transmitter, a transmission channel associated therewith, a plurality of switching stations each having signal responsive switching means associated with said channel, a plurality of lines connectable to said channel'at each switching station, a receiving station associated with each of said lines, a plurality of relays at each station selectively operable by the switching means thereat upon response of said switching means to assigned code signals, line connecting elements controlled by the relays at each switching station for connecting the associated lines to said channels, a locking circuit for each of said relays including break contacts controlled by all others of said relays at the same switching station whereby the operation of one of said relays at a switching station unlocks any one of them at that station that is locked in operated condition, and a locking circuit interrupter operable directly by each of said switching means upon response thereof to a code signal assigned to efiect the operation of a relay at any other switching station for interrupting the locking circuits of the relays associated with that switching means.

5. In a telegraph switching system, a transmitter, a transmission channel associated therewith, a plurality of switching stations each having signal responsive switching means associated with said channel, a plurality of lines connectable to said channel at each of said switching stations, a receiving station associated with each of said lines, means controlled by the switching means at each switching station for selectively connecting the lines of that switching station to said channel, means operable by each of said connecting means at a switching station for disconnecting any other line then connected to said channel at that switching station, and switching elements at each switching station for disconnecting any connected one of its lines upon response of its switching means to signals assigned to connect one of the lines of another switching station.

CHARLES ROBERT WALKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Aug. 2, 1917 

